Screw driving tool



Feb, 1 19%? Filed July 12, 1965 M. WALTON 3,32,672

S CREW DR IVING TOOL INVENTOR.

Marvin Walfon United States Patent 3,302,672 SCREW DRIVING TOOL MarvinWalton, 134 Tuscaloosa Ave, Atherton, Calif. 94025 Filed .Iuly 12, 1965,Ser. No. 471,152 6 Claims. (Cl. 14550) The present invention relates toscrew driving tools. More particularly, the present invention relates todriving tools for screws of the type known as one-way screws orirretrievable screws.

The present invention relates particularly to drive tools forround-headed one-way screws that are provided with indentations orexcisions along diametrically opposite circumferential areas of theirrounded heads which end in abutment surfaces that are located in acommon plane containing the axis of the screw. To effectively engage anddrive such screws into position, the driving tool must have driveelements capable of bearing against both said abutment surfaces. In adirection opposite to the direction in which the screw is to be driveninto position, the floors and/or side walls of the circumferentialindentations or excisions are shaped in such a manner that upon reversalin the operation of the drive tool, the tool is cammed out of saidindentations or excisions and cannot effectively engage the screw head.A particularly effective one-way screw designed for operation with highspeed power tools is described in my copending U.S. patent applicationSerial Number 458,604, filed May 25, 1965.

It is an object of my invention to provide an effective screw drivingtool that is particularly suitable for high speed operation with one-wayscrews of the type referred to and which may be smoothly and effectivelyengaged with such screw heads and may be smoothly disengaged from thescrew heads, upon reversal in its operation.

More particularly, it is an object of the invention to provide a drivetool for screws of the type described, that may be engaged with, ordisengaged from, the screw heads without chattering, and without jarringthe operators hand, and which is not likely to mar the screw head and/orthe objects into which screws are driven by its operation.

Still another object of the invention is to provide a screw driving toolof the type referred to, that lends itself readily to mass productionmethods.

These and other objects of the present invention will be apparent fromthe following description of the accompanying drawings which illustratea preferred embodiment thereof and wherein FIGURE 1 is a perspective ofa screw driving bit em bodying my invention and shows below said bit afragmentary perspective of a one-way screw of the type which it isintended to drive;

FIGURE 2 is a side elevation, partly in section, of the screw drivingbit shown in FIGURE 1;

FIGURE 3 is a bottom plan view of the end surface of the screw drivingbit; and

FIGURES 4 and 5 are schematic perspectives of a sphere and of tworadially displaced hemispheres thereof, illustrating the geometricalparameters of the surfaces that define the conformation of the concavityin the end surface of the screw driving bit of the invention.

The screw driving bit of my invention comprises a cylindrical headportion mounted upon the end of a shank or stem 12 by means of which itmay be coupled to the socket of a rotary drive tool. The fiat endsurface 14 of said head contains a shallow rounded recess or concavity15 of a diameter to fit over the head 16 of the screw 18 for which it isdesigned (FIGURE 1). Geometrically, the conformation of said recess isestablished by the top segments 2th,, and 20 of two complementaryhemispheres 22,, and 22 (FIGURE 4) whose ice center points C and C liebelow the end surface 14 of the head Ill and are dis-placed from eachother in a plane P containing the center axis x of the screw driver,along a common diameter d to opposite sides of said axis (FIGURE 5).FIGURE 4 shows the sphere 22 before its halves 22 and 22 are displacedrelative to each other in the manner explained above. In addition to thevertical piane P in which the displacement occurs, said figure indicatesthe horizontal section plane H that separates the segments from thesphere 22 and which coincides with the plane defined by the end surface14 of the screw driving bit. The radii R and R of the base circle ofsaid segments are somewhat smaller than the radius of the cylindricalhead 10 of the screw driver and are about equal to the radius of theintersection line 'L between the ramp 24 of an excision or indentation26 in the head 16 of the one-way screw and the side wall 28 of saidindentation or excision (FIGURE 1); and the degree of diametricaldisplacement of the center points C, and C of the hemispheres 22 and 22is about equal to, or slightly larger than, the radial depth of thefloor or ramp 24 of an excision or indentation in the head of the screwadjacent the abutment surface 30 thereof.

When the concavity in the end face of the screw driver bit is of aconformation as defined hereinbefore, the two relatively displaced,juxtaposed sphere segments 20, and 20,, form inwardly directedcircumferential ledges 32 and 32 that increase gradually in depth in adirection radially of the concavity and terminate in fiat end surfaces34,, and 34 respectively, that lie within the plane P in which thehemispheres are displaced. Said end surfaces are of horn-shape, as bestshown in FIG- URE l, and are the driver surfaces of the tool. In thepreferred embodiment of the invention illustrated in the accompanyingdrawings the inner edges of said ribs 34,, and 34 are beveled as bestshown at 36 in FIGURES 1 and 2; and especially the inwardly directed endcorners 38 of said ribs are preferably chamfered as likewise shown inFIGURE 1 and as also shown in FIGURE 3.

In the preferred embodiment of the invention illustrated in theaccompanying drawings, the driving head is provided with a centeringboss 40 which may be of truncoconical conformation and which rises fromthe bottom of the concavity 15 coaxially with the drive head 10preferably to a level slightly beyond the end surface 14 of the head, asbest shown in FIGURE 2. Such a centering boss facilitates proper coaxialengagement of the screw driver with the screw. Accordingly, the heads ofoneway screws of the type described and illustrated in FIG- URE 1 areusually provided with axially located centering bores or holes 42 ofinverted conical or trunco-conical shape.

A screw driver having a head formed as described above and illustratedin the accompanying drawings, may easily be brought into proper coaxialengagement with the head of a one-way screw of the type exemplified inFIGURE 1. Its driver surfaces 34,, and 34 will effectively engage theabutment surfaces 32 in the head of the screw 18 without chattering orjarring, even though the tool may be in rotation. Due to the smoothlyrounded nature of the concavity 15, of its ribs 32, and 32 and of thecorners 38 of its driver surfaces 34 and 34 the tool will not mar thescrew head or the article into which the screw is to be driven, and itmay readily be disengaged from the screw; and the screw driver will notcause chattering nor jar the operators hand, even when its operation mayhe accidentally reversed, but will smoothly disengage itself from thescrew head. Moreover, the construction of the screw driver bit of myinvention is such that it may be easily manufactured with great accuracyby mass production methods. It is therefore as economical in manufactureas it is dependable, effective and trouble-free in operation.

I claim:

1. A screw driving tool comprising a cylindrical head having an endsurface, said end surface containing a concavity defined by adjacentsegments of two complementary hemispheres, said segments being displacedto opposite sides of the center axis of said head upon said end surfaceto form with said end surface a pair of oppositely located, inwardlyprojecting ribs terminating in driver surfaces located at either side ofsaid center axis in a common plane containing said axis.

2. A screw driving tool according to claim 1, wherein the inwardlypointing corners of said ribs are chamfered.

3. A screw driving tool according to claim 1, wherein the inner edges ofsaid ribs are beveled.

4. A screw driving tool according to claim 1, including a centering bossrising coaxially with the center axis of said head from the bottom ofsaid concavity.

5. A screw driving tool according to claim 1, including a trunco-conicalcentering boss rising coaxially with the center axis of said head fromthe bottom of said concavity to a level beyond the end surface of saidhead exteriorly of said concavity.

6. A screw driving tool for high speed power operation of one-way screwsof the type described comprising a cylindrical head having a fiat endsurface, said end surface containing a concavity defined by juxtaposedsegments of two complementary hemispheres of equal radii whosegeometrical center points are displaced along a common diameter of thecylindrical surface defined by said head to opposite sides of the centeraXis of said head, said spherical segments defining with said endsurface a pair of oppositely located, inwardly projectingcircumferential ribs of gradually increasing radial depth terminating inhorn-shaped driving surfaces located at either side of said center axisin a common plane containing said center axis.

References Cited by the Examiner UNITED STATES PATENTS 1,956,963 5/1934Salmen 14550 2,180,633 11/1939 Holt 145-50 3,134,292 5/1964 Walton145-50 WILLIAM FELDMAN, Primary Examiner.

R. V. PARKER, JR., Assistant Examiner.

1. A SCREW DRIVING TOOL COMPRISING A CYLINDRICAL HEAD HAVING AN ENDSURFACE, SAID END SURFACE CONTAINING A CONCAVITY DEFINED BY ADJACENTSEGMENTS OF TWO COMPLEMENTARY HEMISPHERES, SAID SEGMENTS BEING DISPLACEDTO OPPOSITE SIDES OF THE CENTER AXIS OF SAID HEAD UPON SAID END SURFACETO FORM WITH SAID END SURFACE A PAIR OF OP-